必须向文本小部件提供非空字符串 - Flutter Android

Question

我的代码运行良好，但现在我无法看到配置文件页面，因为它会生成错误并且我无法识别，即使我尝试在 buildProfileButton() 结束时返回 Container() 但它没有解决问题，因为我稍后更新了该函数的代码。

class Profile extends StatefulWidget {
  final String profileId;

  Profile({this.profileId});

  @override
  _ProfileState createState() => _ProfileState();
}

class _ProfileState extends State<Profile> {
  final String currentUserId = currentUser?.id;
  bool isLoading = false;
  int postCount = 0;
  bool isFollowing = false;
  int followerCount = 0;
  int followingCount = 0;
  List<Post> posts = [];

  @override
  void initState() {
    super.initState();
    getProfilePosts();
    getFollowers();
    getFollowing();
    checkIfFollowing();
  }

  checkIfFollowing() async {
    DocumentSnapshot doc = await followersRef
        .document(widget.profileId)
        .collection('userFollowers')
        .document(currentUserId)
        .get();
    setState(() {
      isFollowing = doc.exists;
    });
  }

  getFollowers() async {
    QuerySnapshot snapshot = await followersRef
        .document(widget.profileId)
        .collection('userFollowers')
        .getDocuments();
    setState(() {
      followerCount = snapshot.documents.length;
    });
  }

  getFollowing() async {
    QuerySnapshot snapshot = await followingRef
        .document(widget.profileId)
        .collection('userFollowing')
        .getDocuments();
    setState(() {
      followingCount = snapshot.documents.length;
    });
  }

  getProfilePosts() async {
    setState(() {
      isLoading = true;
    });
    QuerySnapshot snapshot = await postsRef
        .document(widget.profileId)
        .collection('userPosts')
        .orderBy('rating', descending: true)
        .getDocuments();

    setState(() {
      isLoading = false;
      postCount = snapshot.documents.length;
      posts = snapshot.documents.map((doc) => Post.fromDocument(doc)).toList();
    });
  }

  Column buildCountColumn(String label, int count) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text(
          count.toString(),
          style: TextStyle(fontSize: 22.0, fontWeight: FontWeight.bold),
        ),
        Container(
          margin: EdgeInsets.only(top: 4.0),
          child: Text(
            label,
            style: TextStyle(
              color: Colors.black,
              fontSize: 15.0,
              fontWeight: FontWeight.w400,
            ),
          ),
        ),
      ],
    );
  }

  editProfile() {
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) => EditProfile(currentUserId: currentUserId)));
  }

  Container buildButton({String text, Function function}) {
    return Container(
      padding: EdgeInsets.only(top: 2.0),
      child: FlatButton(
        onPressed: function,
        child: Container(
          width: 210.0,
          height: 27.0,
          child: Text(
            text,
            style: TextStyle(
              color:
                  isFollowing ? Colors.white : Theme.of(context).primaryColor,
              fontWeight: FontWeight.bold,
            ),
          ),
          alignment: Alignment.center,
          decoration: BoxDecoration(
            color: isFollowing ? Theme.of(context).primaryColor : Colors.white,
            border: Border.all(
              color: Theme.of(context).primaryColor,
            ),
            borderRadius: BorderRadius.circular(5.0),
          ),
        ),
      ),
    );
  }

  buildProfileButton() {
    bool isProfileOwner = currentUserId == widget.profileId;
    if (isProfileOwner) {
      return buildButton(
        text: "Edit Profile",
        function: editProfile,
      );
    } else if (isFollowing) {
      return buildButton(
        text: "Unfollow",
        function: handleUnfollowUser,
      );
    } else if (!isFollowing) {
      return buildButton(
        text: "Follow",
        function: handleFollowUser,
      );
    }
  }

  handleUnfollowUser() {
    setState(() {
      isFollowing = false;
    });
    followersRef
        .document(widget.profileId)
        .collection('userFollowers')
        .document(currentUserId)
        .get()
        .then((doc) {
      if (doc.exists) {
        doc.reference.delete();
      }
    });

    followingRef
        .document(currentUserId)
        .collection('userFollowing')
        .document(widget.profileId)
        .get()
        .then((doc) {
      if (doc.exists) {
        doc.reference.delete();
      }
    });

    activityFeedRef
        .document(widget.profileId)
        .collection('feedItems')
        .document(currentUserId)
        .get()
        .then((doc) {
      if (doc.exists) {
        doc.reference.delete();
      }
    });
  }

  handleFollowUser() {
    setState(() {
      isFollowing = true;
    });
    followersRef
        .document(widget.profileId)
        .collection('userFollowers')
        .document(currentUserId)
        .setData({});

    followingRef
        .document(currentUserId)
        .collection('userFollowing')
        .document(widget.profileId)
        .setData({});

    activityFeedRef
        .document(widget.profileId)
        .collection('feedItems')
        .document(currentUserId)
        .setData({
      "type": "follow",
      "ownerId": widget.profileId,
      "username": currentUser.username,
      "userId": currentUserId,
      "userProfileImg": currentUser.photoUrl,
      "timestamp": timestamp,
    });
  }

  buildProfileHeader() {
    return FutureBuilder(
      future: usersRef.document(widget.profileId).get(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          return circularProgress();
        }
        User user = User.fromDocument(snapshot.data);
        return Padding(
          padding: EdgeInsets.all(16.0),
          child: Column(
            children: <Widget>[
              Row(
                children: <Widget>[
                  CircleAvatar(
                    radius: 40.0,
                    backgroundColor: Colors.grey,
                    backgroundImage: CachedNetworkImageProvider(user.photoUrl),
                  ),
                  Expanded(
                    flex: 1,
                    child: Column(
                      children: <Widget>[
                        Row(
                          mainAxisSize: MainAxisSize.max,
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: <Widget>[
                            buildCountColumn("Videos", postCount),
                            buildCountColumn("Followers", followerCount),
                            buildCountColumn("Following", followingCount),
                          ],
                        ),
                        Row(
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: <Widget>[buildProfileButton()],
                        ),
                      ],
                    ),
                  ),
                ],
              ),
              Container(
                alignment: Alignment.centerLeft,
                padding: EdgeInsets.only(top: 12.0),
                child: Text(
                  user.username,
                  style: TextStyle(
                    fontWeight: FontWeight.bold,
                    fontSize: 16.0,
                  ),
                ),
              ),
              Container(
                alignment: Alignment.centerLeft,
                padding: EdgeInsets.only(top: 4.0),
                child: Text(
                  user.displayName,
                  style: TextStyle(
                    fontWeight: FontWeight.bold,
                  ),
                ),
              ),
              Container(
                alignment: Alignment.centerLeft,
                padding: EdgeInsets.only(top: 2.0),
                child: Text(
                  user.bio,
                ),
              ),
            ],
          ),
        );
      },
    );
  }

  buildProfilePosts() {
    if (isLoading) {
      return circularProgress();
    } else if (posts.isEmpty) {
      return Container(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SvgPicture.asset('assets/images/no_content.svg', height: 260.0),
            Padding(
              padding: EdgeInsets.only(top: 20.0),
              child: Text(
                "No Posts",
                style: TextStyle(
                    color: Colors.redAccent,
                    fontSize: 40.0,
                    fontWeight: FontWeight.bold),
              ),
            ),
          ],
        ),
      );
    }

    return Column(
      children: posts,
    );
  }

  buildTogglePostOrientation() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[
        IconButton(
          icon: Icon(Icons.videocam,
              size: 30.0, color: Theme.of(context).primaryColor),
          onPressed: null,
        ),
      ],
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: header(context, titleText: "PROFILE"),
      body: ListView(
        children: <Widget>[
          buildProfileHeader(),
          Divider(),
          buildTogglePostOrientation(),
          Divider(
            height: 0.0,
          ),
          buildProfilePosts(),
        ],
      ),
    );
  }
}

调试控制台说：必须向文本小部件提供非空字符串。 'package:flutter/src/widgets/text.dart': 断言失败：第 285 行 pos 10: 'data != null'

相关的导致错误的小部件是 未来建造者

Answer 1

不要写Text(description)，而是写Text(description ?? '')，这样如果描述为空，文本小部件将为空。

使用对象的属性时，如果user 或user.bio 为空，则不要编写Text(user.bio)，而是为Text 小部件编写Text(user?.bio ?? '') 以获取空字符串。

您还可以确保您在 Text 小部件中使用的字符串永远不会为空。

与问题无关，但我看到您使用了很多功能来构建您的 UI， 我建议您将它们中的每一个都转换为单独的小部件以提高应用程序的性能。请参阅此post 了解更多信息。